dillon1000/react

Use undici polyfill for tests in old Node versions (#28887)

We currently don't test FormData / File dependent features in CI because
we use an old Node.js version in CI. We should probably upgrade to 18
since that's really the minimum version that supports all the features
out of the box.

JSDOM is not a faithful/compatible implementation of these APIs. The
recommended way to use Flight together with FormData/Blob/File in older
Node.js versions, is to polyfill using the `undici` library.

However, even in these versions the Blob implementation isn't quite
faithful so the Reply client needs a slight tweak for multi-byte typed
arrays.